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/**
This file has as its value the list of overlays, as determined from the environment.
If Nix evaluation is [pure](https://nix.dev/manual/nix/latest/command-ref/conf-file.html?highlight=pure-eval#conf-pure-eval), then the list is empty.
*/
let
# Return ‘x’ if it evaluates, or ‘def’ if it throws an exception.
try =
x: def:
let
res = builtins.tryEval x;
in
if res.success then res.value else def;
homeDir = builtins.getEnv "HOME";
isDir = path: builtins.pathExists (path + "/.");
pathOverlays = try (toString <nixpkgs-overlays>) "";
homeOverlaysFile = homeDir + "/.config/nixpkgs/overlays.nix";
homeOverlaysDir = homeDir + "/.config/nixpkgs/overlays";
overlays =
path:
# check if the path is a directory or a file
if isDir path then
# it's a directory, so the set of overlays from the directory, ordered lexicographically
let
content = builtins.readDir path;
in
map (n: import (path + ("/" + n))) (
builtins.filter (
n:
(
builtins.match ".*\\.nix" n != null
&&
# ignore Emacs lock files (.#foo.nix)
builtins.match "\\.#.*" n == null
)
|| builtins.pathExists (path + ("/" + n + "/default.nix"))
) (builtins.attrNames content)
)
else
# it's a file, so the result is the contents of the file itself
let
overlay = import path;
in
if builtins.isFunction overlay then [ overlay ] else overlay;
in
if pathOverlays != "" && builtins.pathExists pathOverlays then
overlays pathOverlays
else if builtins.pathExists homeOverlaysFile && builtins.pathExists homeOverlaysDir then
throw ''
Nixpkgs overlays can be specified with ${homeOverlaysFile} or ${homeOverlaysDir}, but not both.
Please remove one of them and try again.
''
else if builtins.pathExists homeOverlaysFile then
if isDir homeOverlaysFile then
throw (homeOverlaysFile + " should be a file")
else
overlays homeOverlaysFile
else if builtins.pathExists homeOverlaysDir then
if !(isDir homeOverlaysDir) then
throw (homeOverlaysDir + " should be a directory")
else
overlays homeOverlaysDir
else
[ ]
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